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<p><code><strong>add()</strong></code> 方法用来向一个 <code>Set</code> 对象的末尾添加一个指定的值。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code><em>mySet</em>.add(value);</code></code></pre>
<h3 id="参数">参数</h3>
<dl>
<dt>value</dt>
<dd>必需。需要添加到 <code>Set </code>对象的元素的值。</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p><code>Set</code> 对象本身</p>
<p>注意：不能添加重复的值</p>
<h2 id="Examples" name="Examples">示例</h2>
<pre><code  class="language-javascript">var mySet = new Set();

mySet.add(1);
mySet.add(5).add("some text"); // 可以链式调用

console.log(mySet);
// Set [1, 5, "some text"]

mySet.add(5).add(1);
console.log(mySet);
//Set [1, 5]  // 重复的值没有被添加进去</code></pre>
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<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-set.prototype.add" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Set.prototype.add</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-set.prototype.add" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Set.prototype.add</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
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<div id="compat-desktop">
<table class="compat-table">
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<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>38</td>
<td><a href="/en-US/Firefox/Releases/13" title="Released on 2012-06-05.">13.0</a> (13.0)</td>
<td>11</td>
<td>25</td>
<td>7.1</td>
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<div id="compat-mobile">
<table class="compat-table">
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<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
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<tr>
<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td>38</td>
<td>13.0 (13.0)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>8</td>
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</tbody>
</table>
</div>
<h2 id="火狐备注">火狐备注</h2>
<ul>
<li>低于 Firefox 33 (Firefox 33 / Thunderbird 33 / SeaMonkey 2.30)的版本，<code>Set.prototype.add</code> 会返回<code>undefined 并且不可链式调用。</code> 该问题(<a class="external" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1031632" rel="noopener" title="FIXED: Map.prototype.set, WeakMap.prototype.set and Set.prototype.add should be chainable">bug 1031632</a>)已修复。Chrome/v8 中也有该问题 (<a class="external" href="https://code.google.com/p/v8/issues/detail?id=3410" rel="noopener">issue</a>).</li>
</ul>
<h2 id="相关链接">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/Set" title="Set 对象允许你存储任何类型的唯一值，无论是原始值或者是对象引用。"><code>Set</code></a></li>
<li><a href="Reference/Global_Objects/Set/delete" title="delete() 方法可以从一个 Set 对象中删除指定的元素。"><code>Set.prototype.delete()</code></a></li>
<li><a href="Reference/Global_Objects/Set/has" title="has() 方法返回一个布尔值来指示对应的值value是否存在Set对象中。"><code>Set.prototype.has()</code></a></li>
</ul>
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